Molecular and mechanistic characterization of platelet-activating factor-like bioactivity produced upon LDL oxidation

• Published in: Journal of lipid research 2005-09, Vol.46 (9), p.1923-1932
• Main Authors: Androulakis, Nicolaos, Durand, Herve, Ninio, Ewa, Tsoukatos, Demokritos C
• Format: Article
• Language: English
• Subjects: atherogenesis; Chromatography, High Pressure Liquid; Humans; Lipid Peroxidation - drug effects; Lipoproteins, LDL - metabolism; low density lipoprotein; mediators of inflammation; oxidized phospholipids; Platelet Activating Factor - analogs & derivatives; Platelet Activating Factor - analysis; Platelet Activating Factor - pharmacology; Platelet Activating Factor - physiology; platelet-activating factor-acetylhydrolase; platelet-activating factor-transacetylase; Spectrometry, Mass, Electrospray Ionization
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1194/jlr.m500074-jlr200

Oxidation of LDL is thought to be involved in both initiating and sustaining atherogenesis through the formation of proinflammatory lipids and the covalent modification of LDL particles. Platelet-activating factor (PAF; 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent phospholipid mediator involved in inflammation. Upon oxidation of LDL, oxidized phospholipids with PAF-like structure are generated, and some of them may act via the PAF receptor. We evaluated the contribution of 1-0-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) and of other PAF analogs on the PAF-like bioactivity formed upon Cu²⁺-initiated oxidation of LDL. Reverse-phase HPLC purification and electrospray ionization-MS analyses showed that upon oxidation of LDL with inactivated PAF-acetylhydrolase (PAF-AH), C16:0 PAF accounted for >30% of PAF-like biological activity and its sn-2 butenoyl analog accounted for >50%. However, upon LDL oxidation in the presence of exogenous 1-0-alkyl-sn-glycero-3-phosphocholine (lyso-PAF) without PAF-AH inactivation, C16:0 PAF formation accounted for >90% of the biological activity recovered. We suggest that the C16:0 PAF, despite being a minor constituent of the LDL peroxidation products, may contribute substantially to the bioactivity formed in oxidized LDL. The higher bioactivity of C16:0 PAF, and the higher selectivity of the LDL-attached lyso-PAF transacetylase toward very short acyl chains [acetate (C2) vs. butanate (C4)], may explain the contribution described above.